Abnormal oxygen uptake kinetic responses in women with type II diabetes mellitus

Rosiglitazone improves exercise capacity in individuals with type 2 diabetes

OBJECTIVE

Although exercise is recommended as a cornerstone of treatment for type 2 diabetes, it is often poorly adopted by patients. We have noted that even in the absence of apparent cardiovascular disease, persons with type 2 diabetes have an impaired ability to carry out maximal exercise, and the impairment is correlated with insulin resistance and endothelial dysfunction. We hypothesized that administration of a thiazolidinedione (TZD) agent would improve exercise capacity in type 2 diabetes.

RESEARCH DESIGN AND METHODS

Twenty participants with uncomplicated type 2 diabetes were randomly assigned in a double-blind study to receive either 4 mg/day of rosiglitazone or matching placebo after baseline measurements to assess endothelial function (brachial artery diameter by brachial ultrasound), maximal oxygen consumption (VO(2max)), oxygen uptake (VO(2)) kinetics, and insulin sensitivity by hyperinsulinemic-euglycemic clamp. Measurements were reassessed after 4 months of treatment.

RESULTS

Participant groups did not differ at baseline in any measure. Rosiglitazone-treated participants (n = 10) had significantly improved VO(2max) (19.8 +/- 5.3 ml . kg(-1) . min(-1) before rosiglitazone vs. 21.2 +/- 5.1 ml . kg(-1) . min(-1) after rosiglitazone, P < 0.01), insulin sensitivity, and endothelial function. A change in VO(2max) correlated with improved insulin sensitivity measured by clamp (r = 0.68, P < 0.05) and with improved brachial artery diameter (r = 0.70, P < 0.05). Placebo-treated participants (n = 10) showed no changes in VO(2max) (19.4 +/- 5.2 ml . kg(-1) . min(-1) before rosiglitazone vs. 18.1 +/- 5.3 ml . kg(-1) . min(-1) after rosiglitazone, NS) or brachial artery diameter.

CONCLUSIONS

This is the first known report showing that a TZD improved exercise function in type 2 diabetes. Whether this is due to the observed improvements in insulin sensitivity and/or endothelial function or to another action of the TZD class requires further exploration.

Muscle blood flow–O2 uptake interaction and their relation to on-exercise dynamics of O2 exchange

A computer model was developed to provide a theoretical framework for interpreting the dynamics of muscle capillary O(2) exchange in health and disease. We examined the effects of different muscle oxygen uptake (V O(2m)) and CvO(2) profiles on muscle blood flow (Q (m)) kinetics (Q (m)=V O(2m)/[CaO(2)-CvO(2)]). Further, we simulated V O(2m) and Q (m) responses to predict the CvO(2) profile and the underlying dynamics of capillary O(2) exchange (CvO(2)=CaO(2)-V O(2m)/Q (m)). Exponential equations describing V O(2m), CvO(2) and Q (m) responses in vivo were used in the simulations. The results indicated that Q (m) kinetics were relatively insensitive to CvO(2) parameters, but directly associated with V O(2m) kinetics. The biphasic Q (m) response produced a substantial fall in CvO(2) within the first 15-20s of the exercise transition (phase 1 of Q (m)). These results revealed that the main determinant of CvO(2) (or O(2) extraction) kinetics was the dynamic interaction of Q (m) and V O(2m) kinetics during phase 1 of Q (m).

Does aerobic fitness influence microvascular function in healthy adults at risk of developing Type 2 diabetes?

AIM

To investigate whether aerobic fitness is associated with skin microvascular function in healthy adults with an increased risk of developing Type 2 diabetes.

METHODS

Twenty-seven healthy normal glucose-tolerant humans with either a previous diagnosis of gestational diabetes or having two parents with Type 2 diabetes and 27 healthy adults who had no history of diabetes were recruited. Maximal oxygen uptake was assessed using an incremental exercise test to exhaustion. Skin microvascular function was assessed using laser Doppler techniques as the maximum skin hyperaemic response to a thermal stimulus (maximum hyperaemia) and the forearm skin blood flow response to the iontophoretic application of acetylcholine (ACh) and sodium nitroprusside.

RESULTS

Maximal oxygen uptake was not significantly different in the 'at-risk' group compared with healthy controls. Maximum hyperaemia was reduced in those 'at risk' (1.29 +/- 0.30 vs. 1.46 +/- 0.33 V, P = 0.047); however, the peak response to acetylcholine or sodium nitroprusside did not differ in the two groups. A significant positive correlation was demonstrated between maximal oxygen uptake and maximum hyperaemia (r = 0.52, P = 0.006 l/min and r = 0.60, P = 0.001 ml/kg/min) and peak ACh response (r = 0.40, P = 0.04 l/min and r = 0.47, P = 0.013 ml/kg/min) in the 'at-risk' group when expressed in absolute (l/min) or body mass-related (ml/kg/min) terms. No significant correlations were found in the control group.

CONCLUSIONS

In this 'at-risk' group with skin microvascular dysfunction maximal oxygen uptake was not reduced compared with healthy controls. However, in the 'at-risk' group alone, individuals with higher levels of aerobic fitness also had better microvascular and endothelial responsiveness.

Up-regulation of PPARγ coactivator-1α as a strategy for preventing and reversing insulin resistance and obesity

Excessive accumulation of triglycerides and certain fatty acid derivatives in skeletal muscle and other tissues appears to mediate many of the adverse effects of insulin resistance syndrome. Although fatty diets and obesity can promote such accumulation, deficient capacity for fatty acid oxidation can also contribute in this regard. Indeed, in subjects who are insulin resistant, diabetic, and/or obese, fatty acid oxidation by skeletal muscle tends to be inefficient, reflecting decreased expression of mitochondria and mitochondrial enzymes in muscle. This phenomenon is not corrected by weight loss, is not simply reflective of subnormal physical activity, and is also seen in lean first-degree relatives of diabetics; thus, it appears to be primarily attributable to genetic factors. Recent studies indicate that decreased expression of PPARgamma coactivator-1alpha (PGC-1alpha), a "master switch" which induces mitochondrial biogenesis by supporting the transcriptional activity of the nuclear respiratory factors, may largely account for the diminished oxidative capacity of subjects prone to insulin resistance. Thus, feasible measures which up-regulate PGC-1alpha may be useful for preventing and treating insulin resistance and obesity. These may include exercise training, metformin and other agents which stimulate AMP-activated kinase, high-dose biotin, and PPARdelta agonists. Drugs which are specific agonists for PPARdelta show remarkable efficacy in rodent models of insulin resistance, diabetes, and obesity, and are currently being evaluated clinically. Phytanic acid, a branched-chain fatty acid found in omnivore diets, can also activate PPARdelta, and thus should be examined with respect to its impact on mitochondrial biogenesis and insulin sensitivity.

Factors determining the oxygen consumption rate (VO2) on-kinetics in skeletal muscles

Using a computer model of oxidative phosphorylation developed previously [Korzeniewski and Mazat (1996) Biochem. J. 319, 143-148; Korzeniewski and Zoladz (2001) Biophys. Chem. 92, 17-34], we analyse the effect of several factors on the oxygen-uptake kinetics, especially on the oxygen consumption rate (VO2) and half-transition time t(1/2), at the onset of exercise in skeletal muscles. Computer simulations demonstrate that an increase in the total creatine pool [PCr+/-Cr] (where Cr stands for creatine and PCr for phosphocreatine) and in glycolytic ATP supply lengthen the half-transition time, whereas increase in mitochondrial content, in parallel activation of ATP supply and ATP usage, in oxygen concentration, in proton leak, in resting energy demand, in resting cytosolic pH and in initial alkalization decrease this parameter. Theoretical studies show that a decrease in the activity of creatine kinase (CK) [displacement of this enzyme from equilibrium during on-transient (rest-to-work transition)] accelerates the first stage of the VO2 on-transient, but slows down the second stage of this transient. It is also demonstrated that a prior exercise terminated a few minutes before the principal exercise shortens the transition time. Finally, it is shown that at a given ATP demand, and under conditions where CK works near the thermodynamic equilibrium, the half-transition time of VO2 kinetics is determined by the amount of PCr that has to be transformed into Cr during rest-to-work transition; therefore any factor that diminishes the difference in [PCr] between rest and work at a given energy demand will accelerate the VO2 on-kinetics. Our conclusions agree with the general idea formulated originally by Easterby [(1981) Biochem. J. 199, 155-161] that changes in metabolite concentrations determine the transition times between different steady states in metabolic systems.

Exercise training increases glycogen synthase activity and GLUT4 expression but not insulin signaling in overweight nondiabetic and type 2 diabetic subjects

Exercise training improves insulin sensitivity in subjects with and without type 2 diabetes. However, the mechanism by which this occurs is unclear. The present study was undertaken to determine how improved insulin signaling, GLUT4 expression, and glycogen synthase activity contribute to this improvement. Euglycemic clamps with indirect calorimetry and muscle biopsies were performed before and after 8 weeks of exercise training in 16 insulin-resistant nondiabetic subjects and 6 type 2 diabetic patients. Training increased peak aerobic capacity (Vo(2peak)) in both nondiabetic (from 34 +/- 2 to 39 +/- 2 mL O(2)/kg fat-free mass [FFM]/min, 14% +/- 2%, P <.001) and diabetic (from 26 +/- 3 to 34 +/- 3 mL O(2)/kg FFM/min, 32% +/- 4%) subjects. Training also increased insulin-stimulated glucose disposal in nondiabetic (from 6.2 +/- 0.5 to 7.1 +/- 0.7 mg/kg FFM/min) and diabetic subjects (from 4.3 +/- 0.6 to 5.5 +/- 0.6 mg/kg FFM/min). Total glycogen synthase activity was increased by 46% +/- 17% and 45% +/- 12% in nondiabetic and diabetic subjects, respectively, in response to training (P <.01 v before training). Moreover, after training, glycogen synthase fractional velocity was correlated with insulin-stimulated glucose storage (r = 0.53, P <.05) and the training-induced improvement in glucose disposal was accounted for primarily by increased insulin-stimulated glucose storage. Training also increased GLUT4 protein by 38% +/- 8% and 22% +/- 10% in nondiabetic and diabetic subjects, respectively (P <.05 v. before training). Akt protein expression, which was decreased by 29% +/- 3% (P <.05) in the diabetic subjects before training (compared to the nondiabetics), increased significantly in both groups (P <.001). In contrast, exercise training did not enhance the ability of insulin to stimulate insulin receptor substrate-1 (IRS-1)-associated phosphatidylinositol 3 (PI 3)-kinase activity. The present data are consistent with a working model whereby 8 weeks of exercise training increases insulin-stimulated glucose disposal primarily by increasing GLUT4 protein expression without enhancing insulin-stimulated PI 3-kinase signaling, and that once the glucose enters the myocyte, increased glycogen synthase activity preferentially shunts it into glycogen synthesis.

Low cardiorespiratory fitness is associated with elevated C-reactive protein levels in women with type 2 diabetes

OBJECTIVE

The purpose of this study was to examine differences in novel markers of cardiovascular disease (CVD) in women with type 2 diabetes stratified according to cardiorespiratory fitness.

RESEARCH DESIGN AND METHODS

A total of 28 women (mean age 57 +/- 6 years) with type 2 diabetes who were free from overt CVD were placed into low cardiorespiratory fitness (LCF) or average cardiorespiratory fitness (ACF) groups based on a graded exercise test to exhaustion. A group of eight women without type 2 diabetes were also examined and served as healthy control subjects. The median VO(2peak) value was used as a cutoff for group determination. We assessed both conventional CVD risk factors, including blood pressure, BMI, and lipid profile, as well as novel CVD risk factors, such as left ventricular filling dynamics, arterial stiffness, fasting insulin, and C-reactive protein (CRP).

RESULTS

VO(2peak) values were 69 +/- 14 and 91 +/- 24% of predicted values for sedentary age-matched healthy individuals in the LCF and ACF groups, respectively. BMI was significantly greater in the LCF group (P < 0.05); however, no differences were observed in age, lipid profile, or resting hemodynamics. CRP was 3.3-fold higher in the LCF group (6.3 +/- 41. vs. 1.9 +/- 1.7 mg/l, P < 0.05), whereas other novel markers of CVD were not significantly different between the groups. Significant negative relationships were observed between VO(2peak) and both CRP (r = -0.49) and the homeostasis model assessment index (r = -0.48) (P < 0.05).

CONCLUSIONS

The novel finding of this investigation is that low cardiorespiratory fitness is associated with elevated CRP and reduced fasting glucose control in women with type 2 diabetes.

Novel actions of thiazolidinediones on vascular function and exercise capacity

The endothelium is the first line of defense for maintaining normal vascular function in the vessel wall; however, the endothelium is sensitive to metabolic stress. In patients with insulin resistance or type 2 diabetes mellitus, a set of metabolic insults--namely high plasma levels of glucose and free fatty acids, increased inflammation, dyslipidemia, and hypertension--cause endothelial dysfunction and a transition from an antiatherogenic endothelium to a proatherogenic endothelium. Disruption of endothelial function leads to activation of platelets and macrophages, increased thrombotic potential, transition of macrophages to foam cells, stimulation of cytokine secretion, and proliferation of vascular smooth muscle cells. Insulin-sensitizing agents, such as the thiazolidinediones (TZDs), improve flow-mediated vasodilation, decrease macrophage and smooth muscle cell activation, proliferation, and migration, and decrease plaque formation. The TZDs exert multifaceted effects on the vasculature by regulating the expression of transcription factors and orchestrating whole-gene programs that restore vascular physiology to the healthy state. Exercise training and increased levels of habitual physical activity have therapeutic benefit in terms of both preventing and treating insulin resistance and diabetes. However, this benefit of exercise training and increased physical activity is complicated by the fact that individuals with insulin resistance or type 2 diabetes have decreased maximal exercise capacity or maximal oxygen consumption and have slower oxygen uptake kinetics at the beginning of exercise. Both of these abnormalities contribute to the decreased levels of habitual physical activity observed in patients with diabetes. Preliminary data suggest that TZDs improve measures of cardiac function and exercise capacity, and investigators are assessing the impact of treatment with rosiglitazone on exercise capacity in an ongoing clinical trial.

Oxygen uptake kinetics: old and recent lessons from experiments on isolated muscle in situ

The various mechanisms responsible for ATP resynthesis include phosphocreatine (PCr) hydrolysis, anaerobic glycolysis and oxidative phosphorylation. Among these, the latter represents the most important mechanism of energy provision. However, oxidative phosphorylation is characterized by a lower maximal power and a slow attainment of a steady state in response to increased metabolic demand. The rate of adjustment of oxidative metabolism during metabolic transitions, which can be evaluated on the basis of the analysis of O2 uptake (VO2) kinetics, has implications for exercise tolerance and muscle fatigue. Analysis of VO2 kinetics represents a valid tool for the functional evaluation of healthy subjects, athletes and patients. Over the last 35 years experiments conducted on isolated muscle preparations in situ have allowed us to gain insights into several key aspects of skeletal muscle VO2 kinetics. Their main limiting factor resides in an intrinsic slowness of intracellular oxidative metabolism when adjusting to augmented metabolic needs. The rate of adjustment of oxidative phosphorylation in mitochondria can be functionally related to PCr hydrolysis occurring in the cytoplasm.

Cardiovascular risk in women with type 2 diabetes

Type 2 DM appears to eliminate the relative survival advantage experienced by premenopausal nondiabetic women compared with men with regard to CVD. The role of traditional cardiovascular risk factors, while important, cannot fully account for the disparate increase in CVD among women with type 2 DM compared with nondiabetic women. The interplay between type 2 DM and female hormones may prove important. Other less traditional risk factors such as endothelial dysfunction and impaired fibrinolysis may also play a role. Impairments in cardiovascular exercise performance in women with type 2 DM may provide insight in the future as representative of a pre-CVD state. Future research should focus on the specific causes of CVD in women with DM. In the meantime, it is important to aggressively treat modifiable risk factors in this population (Table 1). The impact of this health problem will continue to increase in our aging society, because a steadily increasing proportion of the population will be women; furthermore, an increasing percentage of these women will have diabetes if current trends continue.

Meta-analysis of the effect of structured exercise training on cardiorespiratory fitness in Type 2 diabetes mellitus

AIMS/HYPOTHESIS

Low cardiorespiratory fitness is a powerful and independent predictor of mortality in people with diabetes. Several studies have examined the effects of exercise on cardiorespiratory fitness in Type 2 diabetic individuals. However, these studies had relatively small sample sizes and highly variable results. Therefore the aim of this study was to systematically review and quantify the effects of exercise on cardiorespiratory fitness in Type 2 diabetic individuals.

METHODS

MEDLINE, EMBASE, and four other databases were searched up to March 2002 for randomized, controlled trials evaluating effects of structured aerobic exercise interventions of 8 weeks or more on cardiorespiratory fitness in adults with Type 2 diabetes. Cardiorespiratory fitness was defined as maximal oxygen uptake (VO(2max)) during a maximal exercise test.

RESULTS

Seven studies, presenting data for nine randomized trials comparing exercise and control groups (overall n=266), met the inclusion criteria. Mean exercise characteristics were as follows: 3.4 sessions per week, 49 min per session for 20 weeks. Exercise intensity ranged from 50% to 75% of VO(2max). There was an 11.8% increase in VO(2max) in the exercise group and a 1.0% decrease in the control group (post intervention standardized mean difference =0.53, p<0.003). Studies with higher exercise intensities tended to produce larger improvements in VO(2max). Exercise intensity predicted post-intervention weighted mean difference in HbA(1c) (r=-0.91, p=0.002) to a larger extent than did exercise volume (r=-0.46, p=0.26).

CONCLUSIONS/INTERPRETATION

Regular exercise has a statistically and clinically significant effect on VO(2max) in Type 2 diabetic individuals. Higher intensity exercise could have additional benefits on cardiorespiratory fitness and HbA(1c).

Impact of aerobic exercise training on age-related changes in insulin sensitivity and muscle oxidative capacity

Insulin resistance increases and muscle oxidative capacity decreases during aging, but lifestyle changes-especially physical activity-may reverse these trends. Here we report the effect of a 16-week aerobic exercise program (n = 65) or control activity (n = 37) performed by men and women aged 21-87 years on insulin sensitivity and muscle mitochondria. Insulin sensitivity, measured by intravenous glucose tolerance test, decreased with age (r = -0.32) and was related to abdominal fat content (r = -0.65). Exercise increased peak oxygen uptake (VO(2peak); 10%), activity of muscle mitochondrial enzymes (citrate synthase and cytochrome c oxidase, 45-76%) and mRNA levels of mitochondrial genes (COX4, ND4, both 66%) and genes involved in mitochondrial biogenesis (PGC-1alpha, 55%; NRF-1, 15%; TFAM, 85%). Exercise also increased muscle GLUT4 mRNA and protein (30-52%) and reduced abdominal fat (5%) and plasma triglycerides (25%). None of these changes were affected by age. In contrast, insulin sensitivity improved in younger people but not in middle-aged or older groups. Thus, the muscle mitochondrial response to 4 months of aerobic exercise training was similar in all age-groups, although the older people did not have an improvement in insulin sensitivity.

Altered energetic properties in skeletal muscle of men with well-controlled insulin-dependent (type 1) diabetes

This study asked whether the energetic properties of muscles are changed by insulin-dependent diabetes mellitus (or type 1 diabetes), as occurs in obesity and type 2 diabetes. We used (31)P magnetic resonance spectroscopy to measure glycolytic flux, oxidative flux, and contractile cost in the ankle dorsiflexor muscles of 10 men with well-managed type 1 diabetes and 10 age- and activity-matched control subjects. Each subject performed sustained isometric muscle contractions lasting 30 and 120 s while attempting to maintain 70-75% of maximal voluntary contraction force. An altered glycolytic flux in type 1 diabetic subjects relative to control subjects was apparent from significant differences in pH in muscle at rest and at the end of the 120-s bout. Glycolytic flux during exercise began earlier and reached a higher peak rate in diabetic patients than in control subjects. A reduced oxidative capacity in the diabetic patients' muscles was evident from a significantly slower phosphocreatine recovery from a 30-s exercise bout. Our findings represent the first characterization of the energetic properties of muscle from type 1 diabetic patients. The observed changes in glycolytic and oxidative fluxes suggest a diabetes-induced shift in the metabolic profile of muscle, consistent with studies of obesity and type 2 diabetes that point to common muscle adaptations in these diseases.

Reduced exercise arteriovenous O2 difference in Type 2 diabetes

Maximal O(2) consumption (Vo(2 max)) is lower in individuals with Type 2 diabetes than in sedentary nondiabetic individuals. This study aimed to determine whether the lower Vo(2 max) in diabetic patients was due to a reduction in maximal cardiac output (Q(max)) and/or peripheral O(2) extraction. After 11 Type 2 diabetic patients and 12 nondiabetic subjects, matched for age and body composition, who had not exercised for 2 yr, performed a bicycle ergometer exercise test to determine Vo(2 max), submaximal cardiac output, Q(max), and arterial-mixed venous O(2) (a-v O(2)) difference were assessed. Maximal workload, Vo(2 max), and maximal a-v O(2) difference were lower in Type 2 diabetic patients (P < 0.05). Q(max) was low in both groups but not significantly different: 11.2 and 10.0 l/min for controls and diabetic patients, respectively (P > 0.05). Submaximal O(2) uptake and heart rate were lower at several workloads in diabetic patients; respiratory exchange ratio was similar between groups at all workloads. Vo(2 max) was linearly correlated with a-v O(2) difference, but not Q(max) in diabetic patients. These data suggest that a reduction in maximal a-v O(2) difference contributes to a decreased Vo(2 max) in Type 2 diabetic patients.

Dynamics of oxygen uptake following exercise onset in rat skeletal muscle

Technical limitations have precluded measurement of the V(O(2)) profile within contracting muscle (mV(O(2))) and hence it is not known to what extent V(O(2)) dynamics measured across limbs in humans or muscles in the dog are influenced by transit delays between the muscle microvasculature and venous effluent. Measurements of capillary red blood cell flux and microvascular P(O(2)) (P(O(2)m)) were combined to resolve the time course of mV(O(2)) across the rest-stimulation transient (1 Hz, twitch contractions). mV(O(2)) began to rise at the onset of contractions in a close to monoexponential fashion (time constant, J = 23.2 +/- 1.0 sec) and reached it's steady-state value at 4.5-fold above baseline. Using computer simulation in healthy and disease conditions (diabetes and chronic heart failure), our findings suggest that: (1) mV(O(2)) increases essentially immediately (< 2 sec) following exercise onset; (2) within healthy muscle the J blood flow (thus O(2) delivery, J Q(O(2)m)) is faster than JmV(O(2)) such that oxygen delivery is not limiting, and 3) a faster P(O(2)m) fall to a P(O(2)m) value below steady-state values within muscle from diseased animals is consistent with a relatively sluggish Q(O(2)m) response compared to that of mV(O(2)).

Current concepts in insulin resistance, type 2 diabetes mellitus, and the metabolic syndrome

A clustering of risk factors, including elevated triglycerides, decreased high-density lipoprotein cholesterol, hyperinsulinemia, and hypertension often are observed in patients who are insulin resistant. Insulin resistance has been found to play a critical role in the development of cardiovascular disease, particularly in patients with type 2 diabetes. Patients with insulin resistance have an increase in small, dense low-density lipoprotein (LDL) cholesterol, which is more atherogenic than large, buoyant LDL cholesterol. In the context of insulin resistance, insulin has reduced effects on the phosphatidylinositol 3 kinase (PI3K) pathway, whereas mitogen-activated protein kinase activity is maintained. The result is an exaggeration of the mitogenic actions of insulin leading to vascular smooth muscle proliferation and elevated plasminogen activator inhibitor (PAI)-1. Notably, nitric oxide-mediated vasodilation also is impaired, further contributing to atherogenicity. In addition, hyperinsulinemia further contributes to cardiovascular risk by promoting thrombosis. Patients who are insulin resistant have decreased fibrinolysis, as indicated by increased levels of PAI-1. Studies have shown that enhancing insulin sensitivity with insulin sensitizers, such as thiazolidinediones, may improve insulin resistance and limit the development of adverse cardiovascular consequences.

Dynamics of microvascular oxygen pressure during rest-contraction transition in skeletal muscle of diabetic rats

Type I diabetes reduces dramatically the capacity of skeletal muscle to receive oxygen (QO(2)). In control (C; n = 6) and streptozotocin-induced diabetic (D: n = 6, plasma glucose = 25.3 +/- 3.9 mmol/l and C: 8.3 +/- 0.5 mmol/l) rats, phosphorescence quenching was used to test the hypothesis that, in D rats, the decline in microvascular PO(2) [Pm(O(2)), which reflects the dynamic balance between O(2) utilization (VO(2)) and QO(2)] of the spinotrapezius muscle after the onset of electrical stimulation (1 Hz) would be faster compared with that of C rats. Pm(O(2)) data were fit with a one or two exponential process (contingent on the presence of an undershoot) with independent time delays using least-squares regression analysis. In D rats, Pm(O(2)) at rest was lower (C: 31.2 +/- 3.2 mmHg; D: 24.3 +/- 1.3 mmHg, P < 0.05) and at the onset of contractions decreased after a shorter delay (C: 13.5 +/- 1.8 s; D: 7.6 +/- 2.1 s, P < 0.05) and with a reduced mean response time (C: 31.4 +/- 3.3 s; D: 23.9 +/- 3.1 s, P < 0.05). Pm(O(2)) exhibited a marked undershoot of the end-stimulation response in D muscles (D: 3.3 +/- 1.1 mmHg, P < 0.05), which was absent in C muscles. These results indicate an altered VO(2)-to-QO(2) matching across the rest-exercise transition in muscles of D rats.

Synthesis rate of muscle proteins, muscle functions, and amino acid kinetics in type 2 diabetes

Improvement of glycemic status by insulin is associated with profound changes in amino acid metabolism in type 1 diabetes. In contrast, a dissociation of insulin effect on glucose and amino acid metabolism has been reported in type 2 diabetes. Type 2 diabetic patients are reported to have reduced muscle oxidative enzymes and VO(2max). We investigated the effect of 11 days of intensive insulin treatment (T(2)D+) on whole-body amino acid kinetics, muscle protein synthesis rates, and muscle functions in eight type 2 diabetic subjects after withdrawing all treatments for 2 weeks (T(2)D-) and compared the results with those of weight-matched lean control subjects using stable isotopes of the amino acids. Whole-body leucine, phenylalanine and tyrosine fluxes, leucine oxidation, and plasma amino acid levels were similar in all groups, although plasma glucose levels were significantly higher in T(2)D-. Insulin treatment reduced leucine nitrogen flux and transamination rates in subjects with type 2 diabetes. Synthesis rates of muscle mitochondrial, sarcoplasmic, and mixed muscle proteins were not affected by glycemic status or insulin treatment in subjects with type 2 diabetes. Muscle strength was also unaffected by diabetes or glycemic status. In contrast, the diabetic patients showed increased tendency for muscle fatigability. Insulin treatment also failed to stimulate muscle cytochrome C oxidase activity in the diabetic patients, although it modestly elevated citrate synthase. In conclusion, improvement of glycemic status by insulin treatment did not alter whole-body amino acid turnover in type 2 diabetic subjects, but leucine nitrogen flux, transamination rates, and plasma ketoisocaproate level were decreased. Insulin treatments in subjects with type 2 diabetes had no effect on muscle mitochondrial protein synthesis and cytochrome C oxidase, a key enzyme for ATP production.

Effects of exercise training on aerobic and functional capacity of end-stage renal disease patients

The aim was to assess the effects of exercise training on aerobic and fuctional capacity of patients with end-stage renal disease (ESRD). Patients completed an incremental exercise test on a cycle ergometer to determine VO2 peak and VO2 at ventilatory threshold (VT; V-slope). On a separate day they performed two constant load exercise tests on a cycle ergometer at 90% of VT and at a workload of 33 W, to determine VO2 kinetics. Functional capacity was assessed using measurements of sit-to-stands (STS-5, STS-60) and a walk test. Dialysis patients were randomly allocated to an exercise (ET: n = 18, age = 57.3 years) or control (C: n = 15, age = 50.5 - 5 years) group. The ET group participated in an exercise training programme involving cycling for 3 months. Repeated measures ANOVA revealed significant time by group interactions (P < 0.05) following training for VO2 peak (ET: 17 +/- 6.1 versus 19.9 +/- 6-3, C: 19.5 +/- 4.7 versus 188 +/- 4.9 ml kg min(-1)) and VO2-VT (ET: 10.7 +/- 3.5 versus 11.8 +/- 3.3, C:12.9 +/- 3.2 versus 119 +/- 3.5 ml kg min(-10). VO2 kinetics remained unchanged in both groups at 90% -VT, but a trend (P = 0.059) towards faster kinetics at the 33 W was observed (ET: 49.6 +/- 19.5 versus 37.8 +/- 12.7, C: 42.8 +/- 13 versus 49.4 +/- 20.2 s). Significant time by group interactions (P < 0.05) were also observed for STS-5 (ET: 14.7 +/- 6.2 versus 11.0 +/- 3.3, C: 12.8 +/- 4.4 versus 12.7 +/- 4.8 s) and STS-60 measurements (ET: 21.2 + 7.2 versus 26.9 +/- 6.2, C: 23.7 +/- 6.8 versus 24.1 +/- 7.2). Three months of exercise rehabilitation significantly improves peak exercise capacity of patients with ESRD. Measurements of VO2 kinetics and functional capacity suggest that longer time might be needed to induce peripheral adaptations.

Effect of non-insulin-dependent diabetes mellitus on pulmonary function and exercise tolerance in chronic congestive heart failure

In chronic congestive heart failure (CHF), backward effects of left ventricular dysfunction alter pulmonary volumes and gas diffusion. Some of these disorders are detected in some patients with diabetes mellitus, possibly due to a microangiopathic process and nonenzymatic glycosylation of lung tissue proteins. We explored the possibility that coexistence of non-insulin-dependent diabetes mellitus (NIDDM) may potentiate the deterioration of lung function in CHF. In 20 normoglycemic patients (group 1) and in 20 patients with NIDDM (group 2), with New York Heart Association class II to III CHF due to idiopathic or ischemic cardiac disease, and in 20 controls (groups were age- and gender-matched), we investigated cardiac function, pulmonary volumes, carbon monoxide diffusion (DL(CO)) and its alveolar-capillary membrane (D(M)) subcomponent, oxygen uptake and dead space-to-tidal volume ratio (pVD/VT) at peak exercise (individualized ramp test), and slope of ventilation-to-carbon dioxide production ratio (VE/VCO(2)) during exercise. Although, compared with reference subjects, both patient groups had similar variations in left ventricular diastolic volume, ejection fraction, and pulmonary wedge pressure; in group 2 lung volumes, DL(CO), D(M), and oxygen uptake were significantly more reduced; in this group there was no overlap of individual results of DL(CO) and D(M) with those in controls; VE/VCO(2) slope and pVD/VT also were significantly increased, and inversely correlated with D(M). Thus, coexistence of NIDDM makes pulmonary dysfunction worse in CHF, and significantly enhances exercise intolerance.

Impact of left ventricular diastolic dysfunction on maximal treadmill performance in normotensive subjects with well-controlled type 2 diabetes mellitus

Patients with type 2 diabetes often have impaired exercise capacity compared with nondiabetic subjects. Left ventricular (LV) diastolic dysfunction has been shown to limit exercise performance in nondiabetic subjects. Men with well-controlled type 2 diabetes were divided into 2 groups: normal LV diastolic function (group 1, n = 9) or LV diastolic dysfunction (group 2, n = 10) based on standard echocardiographic criteria using pulmonary veins and transmitral flow recordings. They were matched for age and had no evidence of systemic hypertension, macroalbuminuria, coronary artery disease, congestive heart failure, clinical diabetic complications, and thyroid disease. Good metabolic control was demonstrated by glycated hemoglobin levels of 6.7+/-1.6% and 6.6+/-2.5% (means +/- SD) in patients with LV diastolic dysfunction and in controls, respectively. Each subject performed a symptom-limited modified Bruce protocol treadmill exercise test. Maximal treadmill performance was higher in subjects with normal diastolic function compared with subjects with LV diastolic dysfunction when expressed in time (803+/-29 vs. 662+/-44 seconds, respectively, p<0.02) or in METs (11.4+/-1.2 vs. 9.5+/-1.9 METs, respectively, p<0.02). Moreover, there was a correlation between E/A ratio and exercise duration (r = 0.64, p = 0.004) or E/A ratio and METs (r = 0.658, p = 0.003). There were no significant differences in maximal heart rate, maximal systolic and diastolic blood pressure, or maximal rate-pressure product attained during the exercise test. In conclusion, this study demonstrated that LV diastolic dysfunction influences maximal treadmill performance and could explain lower maximal performance observed in patients with type 2 diabetes.